109 



probably belonged to a different one. Found in association \uith the canines 

 referred to Uintamastix atrox, it may pertain to the same animal. 



Order Rodentia. 



Small quadrupeds with clawed toes. Teeth consisting of two long curved 

 incisors in each jaw ; no canines, and the molars separated from the former 

 by a wide interval. 



Paramys. 



An interesting peculiar extinct genus of gnawers of the sciurine family is 

 indicated by a number of specimens, consisting of fragments of lower jaws 

 with teeth, which were discovered by Dr. Carter, in the summer of 1871, in 

 the Tertiary formation in the vicinity of Fort Bridger. 



As in the squirrels and marmots, the lower molars are four in number, 

 and are inserted each by two fangs. They are nearly of the same size, but 

 are proportionately narrower than in the animals just mentioned, as the fore 

 and aft diameter exceeds the transverse, while in most sciurine animals the 

 reverse condition usually exists. 



The crowns are short, square, tuberculate, and enameled. The arrange- 

 ments and proportionate size of the tubercles at the four corners of the crown, 

 including a concave surface, are the same as in the squirrels. 



The lower jaw is proportionately shorter and deeper than in most known 

 rodents, the reduction in length being mainly due to a less development of 

 that part of the bone in advance of the molars. To compensate for the dif- 

 ference in length and to make room to accommodate the incisors, these teeth 

 reach farther back than usual. In squirrels and marmots their posterior 

 extremity reaches a short distance behind and beneath the last molar. In 

 Paramys it reached further backward, upward, and externally to a level 

 with the crown of the last molar. 



The jaw in advance of the molars is not only short compared with the usual 

 condition in most known rodents, but the acute edge of the hiatus between 

 the molars and incisors is almost on a level with the alveoli of the teeth, 

 instead of forming a deep concave notch, so conspicuous a feature in the lower 

 jaw of the gnawers generally. 



In sciurine and most other rodents the ridge defining the masseteric fossa 

 extends far forward on the side of the jaw to a position beneath the second or 



